Method for manufacturing heat exchangers

ABSTRACT

A heat exchanger having plastic channel plates (10) is manufactured by stacking the plates with intermediate spacer members. The channel plates comprise two outer walls (12, 14) which are interconnected by a plurality of intermediate walls (16). The end-portions of the intermediate walls are melted along a predetermined length thereof, while the end-portions of the outer walls of each channel plate are caused to bend away from one another, such that the edges will form integrated unities with the edges of adjacent end-portions of adjacent channel plates. Prior to solidification of the resultant joins, the joins may be flattened-out with the aid of a roller. According to the invention, the spaces defined by the outer walls of the channel plates and the spacer members may be filled with plastic particles, which form an integrated unity with the end-portions of the channel plates.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing heatexchangers for counter flow, cross flow or parallel flow, wherein theheat exchangers are substansially made up of a plurality of extrudedplastic channel plates, and a heat exchanger produced according to themethod.

BACKGROUND OF THE INVENTION

One such method is described in EP-A1-0 315 052. According to this knownmethod the channel plates are treated in a manner to cause respectiveend portions of the outer walls of the individual channel plates of theheat exchanger to bend outwardly, such that the edges of said outwardlybent end portions will lie in contact with one another or in thevicinity of one another, and are then mutually joined by a weld seam, bygluing or by a U-shaped section fitted over said edges, so as to closethe channels in the transverse channel system, formed with the aid ofspacer members, at the side edges of said channels. The heat exchangermay be coupled for parallel current, counter current or cross currentflow of the heat-exchanging fluids, which may be liquids or gases.

According to one preferred alternative proposed in the aforesaidpublication, a part of the end portions of the intermediate walls ismilled away prior to mutually assembling the channel plates togetherwith intermediate spacer members, so as to expose a desired length ofthe end portions of the outer walls, these exposed end portions thenbeing bent outwards. According to another alternative proposed in theaforesaid publication, the intermediate walls are configured at thechannel-plate manufacturing stage such that the height of theend-portions of said intermediate walls becomes succesively greater thecloser to the edge of the channel plates at the same time as the endportions of the outer walls are given a correspondingly, outwardlycurved or bent form.

This pre-forming of the channel plates involves additional work andtherewith higher manufacturing costs.

Another method of manufacturing a heat exchanger comprising plasticchannel plates is described in EP-0-226 825. The end portions of thechannel plates are fitted into openings provided in two plastic endplates and are therewith held parallel with one another in given spacerelationship. The channel plates are then heat treated so as to melt theends of the narrow long sides and the broad long sides of said plates,causing the channel walls to expand and to fuse to the inner definingsurfaces of said openings. Alternatively, the channel plates may extendslightly freely above the openings in the end plate, so as to enable theends of the channel plates to expand during the heat treatment andthereby lock the channel plates in the end-plate openings. Thus, inorder to produce a separate heat exchanger it is necessary to use twoend plates provided with openings in which the end portions of thechannel plates shall be fitted to desired positions. The end platestogether with their accurately disposed and configured openings involveadditional costs, as does also the task of fitting the channel plates inthe openings provided in said two end walls.

U.S. Pat. No. 4,733,718 and DE-A-2 751 115 describe methods which areeven further distant from the inventive concept than EP-A-226 825, andconsequently the methods taught by these publications will not bediscussed in detail here.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a simpler method ofmanufacture than the aforedescribed known methods, without the need topre-form the channel plates or the need to use additional end platesprovided with openings into which the ends of the channel plates areinserted and then melt-fused together with the walls defining saidopenings.

This object is achieved with the inventive method, in which a pluralityof extruded plastic channel plates are mutually stacked together withintermediate spacer members so as to form a first channel system betweenthe channel plates and to form a second channel system consisting ofchannels in the channel plates, said plates having two outer walls whichare mutually connected by parallel intermediate walls to form the secondchannel system, and in which the end-edges of the outer walls formingrespective channel walls in the first channel system are mutually joinedwith the aid of heat treatment so as to close the channels of the firstchannel system at the side edges of said channels, which method ischaracterized in that the end sides of the plate pack, in the proximityof the ends of the second channel system, are heated with radiation heator with thermal convection heat until a predetermined length of theend-portions of the intermediate walls has melted down and that theend-portions of adjacent outer walls at the same time are caused to bendoutwardly away from one another as a result of changes, due to the heattreatment, in the stresses present in the plastic material, such thatthe essentially semi-liquid end-portions are essentially brought intocontact with the outwardly curved end-portions of the outer walls ofadjacent channel plates and are integated with said outer walls.

The channel plates are extruded in a known manner from a plasticmaterial, preferably polypropylene, although any other material suitablefor carrying-out the inventive method and having correspondingproperties may be used, while utilizing the stresses induced in theplates during their extrusion. It has also been found that translucentplastic materials are especially suitable for the inventive method inthat they have properties that provide better results regardingstrength, and also in that they have a facilitating effect regardingproduction engineering; this is probably due to theese materialscrystalline proporties.

The channel plates are then assembled into a pack with intermediatespacer members and, in accordance with the invention, the channel-platepack is simply moved past an apparatus which delivers radiation heat orthermal convection heat so as to heat the pack at those end surfacesthereof where the channel-ends of the channel plates are located. Theend surfaces are heated to an extent sufficient to bring theend-portions of the channel walls to a given molten state and to bringthe end-portions of the outer walls to a plastic state and the edges toa molten state. Tests have shown that this is possible. The stresses inthe plastic material are evidently changed during the heat treatment, soas to cause the end-portions of the outer walls to bend outwardly fromone another at their respective edges and to form an integrated unitywith the edges of adjacent end-portions. The joins obtained are bothtight and have good strength. The joins may be subjected to pressureduring solidification of the partially plasticized material with the aidof a roller, plate or some other appropriate device in a manner toflatten out the joins and to form a smooth end surface.

The spacer members are preferably disposed in the vicinity of theend-portions of the outer walls prior to the heat treatment, and arepreferably removed after the operation is concluded. The spacer memberscan be heat-absorbing members made of heat-absorbing material, such asaluminum, although any material whith similar properties can be used.They can have the form of strips or plates, or any similar shape.

According to one embodiment of the present invention, at least oneintermediate space defined by the outer surfaces of the outer walls oftwo adjacent channel plates and intermediate spacer members, when thespacer member is disposed in the proximity of the end-portions of theouter walls, can be filled either completely or partially with plasticparticles prior to the heat treatment. The plastic particle filling issecured by the heat treatment, partly through fusion of the particleswith the channel plates. This will further increase the strength of theheat exchanger construction and enable a larger distance between thechannel plates. In this embodiment the position of the spacer membersare adjusted in relation to the end-portions in such a manner that theplastic particle filling gives joins with sufficient strenght in theheat treatment. The extent and nature of this adjustment will inpractise be sufficiently easy to determine for a person skilled in theart.

An other object of the present invention is a heat exchanger produced bythe method according to said invention.

DEFINITIONS

By the term "particle" is in this application meant any suitable formsuch as briquettes, granules, granulates, pellets, grains, beads,tablets and other similar forms that according to a person skilled inthe art can be comprised in the idea or concept of a particle. In apreferred embodiment the plastic particles are in form of a powder, andmost preferred in form of a fine powder suitable for sufficiently fastand even melting. Preferred particle size is from about 0.05 mm to 3 mm,and especially from about 0.05 mm to 1 mm. The particles are preferablymade from a material that according to melting proporties are compatiblewith the channel plate material. The particulate plastic material may,for instance, be of the kind designated "SC 1355 RM" marketed by NestePolyeten AB, Stenungsund, Sweden; this particulate polypropylene plasticmaterial has an estimated melting point of about 160° C. and a particlesize from about 0.1 mm to about 0.8 mm.

The term "integrated" means in this application a state in which theparts or objects, that are integrated, are joined, united, or adhered toeach other through fusion, sticking, tacking, welding, fusion welding,bonding or adhesion or any combination therof, and in the embodiment ofthe present invention comprising plastic particles even sintering, or inany other similar manner known to a person skilled in the art.

The inventive method is described below with reference to non-limiting,exemplifying embodiments thereof and also with reference to theaccompanying drawings, throughout which like designation numbers refersto like objects, which illustrate various steps of non-limiting,exemplifying embodiments of the manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one corner part of a plasticchannel plate.

FIG. 2 illustrates schematically in perspective view one end of achannel-plate pack with intermediate spacer members, prior to the heattreatment.

FIG. 3 illustrates the basic state of the pack shown in FIG. 2 prior tothe heat treatment.

FIG. 4 is a view similar to that of FIG. 3 and shows the pack subsequentto melting of the end-portions of the intermediate walls and subsequentto outward bending of the end-portions of the outer walls caused by theheat treatment, and further shows the end-portions integated withoutwardly curved or bent edges of adjacent end-portions.

FIG. 5 shows the ends of respective outwardly bent end-portionsflattened with the aid of a flattening plate or flattening roller.

FIG. 6 illustrates the finished product, subsequent to having removedthe spacer members.

FIGS. 7 and 8 are views corresponding respectively to the views of FIGS.3 and 4, but with the addition of plastic particles in some of theaforesaid interspaces.

DETAILED DESCRIPTION OF THE INVENTION

The channel plates 10 may, for instance, be of the kind that areextruded from polypropylene, designated "Akylux" (supplied by KayserbergPackaging SA, France) and has two mutually parallel outer walls 12, 14which are interconnected by a plurality of mutually parallelintermediate walls 16 to form through flow channels 18. The thickness ofthe channel plates may vary from about 1.0 mm to about 50 mm.

The end edges of the outer walls are designated 12 A, 14 A while the endedges of the intermediate walls are designated 16 A.

The end-portions of the outer walls are designated 12 B, 14 B, while theend portions of the intermediate walls are designated 16 B.

FIG. 3 illustrates the step of heating the end of the channel plate 10with the aid of a device 20 which radiates heat or delivers thermalconvection heat.

Prior to this heat treatment, a number of channel plates 10 are stackedtogether with spacer members 22 to form channels 24 (FIG. 6), which areintended to extend perpendicular to the channels 18. FIG. 3 is an endview of the resultant pack, with the heating source 20 located adjacentsaid end. The heating source 20 and the pack are moved parallel inrelation to one another, thereby making continuous manufacture possible.

Initial heating of the end-portions 16 B of the intermediate wall 16 inaccordance with the FIG. 3 illustration, causes the end-portions 16 B tomelt and to take a position 16 C, therewith exposing the end-portions 12C, 14 C, which have softened to a plastic or semi-liquid state.

When heating is continued, the end-portions 12 C, 14 C will bendoutwards away from one another to the position illustrated in FIG. 4 andthe edges of said plates will fuse together to form joins 26, thisoutward bending of the end-portions 12 C, 14 C being caused by thechanges that the heat delivered to said end-portions engenders in theextrusion-induced stresses in the channel plates.

FIG. 5 illustrates a pressure roller 28, which is caused to roll overthe end surface of the pack in a manner to flatten the joins 26 of theouter walls, so that the outer surfaces thereof will lie along a flatend surface 30 and form joins 32. In this way the channels 24 areterminated by thickened and therewith relatively strong end walls.Flattening of the joins 26 also provides extremely good measurementaccuracy between the end surfaces of the plate heat exchanger and alsoenhances the ability of the heat exchanger to absorb pressure forces.

As mentioned above, the spaces defined by the channel-plate outer wallsand the spacer members may be filled with plastic particles whencarrying out the inventive method. This is illustrated in FIGS. 7 and 8.In FIG. 7 plastic particles are delivered from a plastic particle source34 into the intermediate spaces defined by the end-portions of the outerwalls 12 B, 14 B and the end edges 22 A of the spacer members. FIG. 8illustrates a situation at some stage during the subsequent heattreatment when the particles and the outwardly bending end-portions ofthe outer walls 12 C, 14 C are forming an integrated unity; asillustrated, the joins can, as an alternative, consist of meltedparticles in combination with the outwardly bending end-portions,without any need for said outwardly bending end-portions to be in directcontact with each other.

We claim:
 1. A method of manufacturing heat exchangers for counter flow,cross flow or parallel flow, which comprises: mutually stacking aplurality of extruded plastic channel plates together withheat-absorbing intermediate spacer members so as to form a first channelsystem between the channel plates and to form a second channel systemconsisting of channels in the channel plates, said plates having twoouter walls which are mutually connected by parallel intermediate wallsto form the second channel system, and wherein the end-edges of theouter walls forming respective channel walls in the first channel systemare mutually joined with the aid of heat treatment so as to close thechannels of the first channel system at the side edges of said channels,heating with one of radiation heat and thermal convection heat the endsides of the plate pack, in the proximity of the ends of the secondchannel system until a predetermined length of the end-portions of theintermediate walls has melted down and at the same time causing theend-portions of adjacent outer walls on a respective channel plate tobend outwardly away from one another as a result of changes, due to theheat treatment and the heat-absorbing intermediate spacer members, inthe stresses present in the plastic material, bringing the essentiallysemi-liquid end-portions into contact with the outwardly bentend-portions of the outer walls of the adjacent channel plates andintegrating said semi-liquid end-portions with said outer walls, andremoving the intermediate spacer members.
 2. A method according to claim1, wherein the channel plates are made of a polypropylene plasticmaterial.
 3. A method according to claim 1, wherein the heat-absorbingintermediate spacer members are disposed in the vicinity of theendportions of the outer walls prior to said heat treatment.
 4. A methodaccording to claim 1, further including flattening the heat-treatedend-portions while said portions are in a heated and plastic state, witha flattening pressure plate or pressure roller.
 5. A method according toclaim 1, wherein the intermediate spacer members have the form ofaluminum strips or aluminum plates.
 6. A heat exchanger produced by amethod according to claim
 1. 7. A method of manufacturing heatexchangers for counter flow, cross flow or parallel flow, whichcomprises: mutually stacking a plurality of extruded plastic channelplates together with heat-absorbing intermediate spacer members so as toform a first channel system between the channel plates and to form asecond channel system consisting of channels in the channel plates, saidplates having two outer walls which are mutually connected by parallelintermediate walls to form the second channel system, and wherein theend-edges of the outer walls forming respective channel walls in thefirst channel system are mutually joined with the aid of heat treatmentso as to close the channels of the first channel system at the sideedges of said channels, introducing from one of the end sides of theplate pack, where the ends of the second channel system are located,plastic particles into at least one of the spaces defined by the outersurfaces of the outer walls of two mutually adjacent channel plates andintermediate spacer members which are disposed in the proximity of theend-portions of the outer walls, heating said end side with one ofradiation heat and thermal convection heat until a given length of theintermediate-wall end-portions has been brought to a given molten state,such that the end-portions of said adjacent outer walls on a respectivechannel plate are caused to bend away from one another as a result ofheat-engendered changes in the stresses in the plastic material and theheat-absorbing intermediate spacer members, and the essentiallysemi-molten end-portions with the plastic particles introducedtherebetween are formed to an integrated unity and essentiallyintegrated with the outwardly bent end-portions of the outer walls ofadjacent channel plates and with the plastic particles, and removing theintermediate spacer members.
 8. A method according to claim 7, whereinthe plastic particles are polypropylene particles.
 9. A method accordingto claim 2, wherein the channel plates are made of a polypropyleneplastic material.
 10. A method according to claim 7, wherein theheat-absorbing intermediate spacer members are disposed in the vicinityof the endportions of the outer walls prior to said heat treatment. 11.A method according to claim 7, further including flattening theheat-treated end-portions while said portions are in a heated andplastic state, with a flattening pressure plate or pressure roller. 12.A method according to claim 7, wherein the heat-absorbing intermediatespacer members have the form of aluminum strips or aluminum plates. 13.A heat exchanger produced by a method according to claim 7.